1. Field of the Invention
The invention relates to a delivery module for a dosage system used to introduce a reducing agent into the exhaust gas tract of an internal combustion engine.
2. Description of the Prior Art
In motor vehicles with internal combustion engines, because of the increasingly stringent laws regarding exhaust gases expected in the next few years, the pollutant NOx contained in the exhaust gas of internal combustion engines must be reduced. One currently used method for this is the SCR process (Selective Catalytic Reduction), in which the pollutant NOx is reduced to N2 or H2O, using liquid reducing agent. The reducing agent used, as a rule in liquid form, is received in a tank and is fed by a delivery module from the tank via a line to a metering module for injecting the reducing agent into the exhaust gas. The goal is to position the metering system, with its components, that is, tank delivery module lines, metering module, and the like, outside the passenger compartment of the motor vehicle, since at elevated temperatures, ammonia (NH3) forms from the aqueous urea solution used as the reducing agent. With this concept of accommodating the entire metering system that carries the reducing agent outside the passenger compartment, it is assured that in the event of leaks in the metering system that carries the reducing agent, or in the event of an accident, no NH3 formation can occur in the passenger compartment. Stringent demands are made of the delivery module, which includes such components as a pressure sensor, pump, scavenging valves, filter, heater, contact means of the components, and the like, in terms of being splashproof and being capable of fording flooded roads, and in particular of having corrosion resistance. Since the components of the metering system that carry the reducing agent are disposed outside the passenger compartment, they are exposed to a greater extent to temperature fluctuations and to the influence of splashing water and de-icing salt, in contrast to a disposition of those components in the passenger compartment.
These demands in terms of being splashproof and having fording ability as well as corrosion resistance are attended to, in systems used until now, by providing that the components of the entire metering system, that is, the aforementioned components comprising the tank delivery module, lines, and metering module, are accommodated in a separate housing. An internal cable harness connects the individual components to a central plug, which is mounted on the housing and by way of which the task of electrical contacting is shifted to the outside. The components accommodated inside the housing communicate with one another hydraulically via heatable hoses. These heatable hoses end at an inlet and outlet piece on the housing and are thus shifted to the hose connections outside the common housing. Once the components are mounted inside this housing, the housing is closed, sealed off from the environment with its components, via a separate lid. In a different concept for meeting this demand, all the components of the delivery module for the system carrying the reducing agent are embodied as individual components that are already splashproof and have fording ability. The individual components are mounted on a circuit board or mounting plate or the like and are sealed off by seals at an interface between the components and the plate. The hydraulic communication of the components is effected inside a plate or mounting block (circuit board). Each individual component designed to be splashproof and capable of fording flooded roads has its own contact means. A heater is also connected to the plate.
The embodiment described at the outset above is relatively large, since the individual components are accommodated in a common housing. Because of the hydraulic communication of the components with one another via hoses and because of the electrical triggering of the individual components with a central plug via a cable harness, the common housing in the first version sketched at the outset is extremely expensive and requires an extremely large amount of space. In addition to the components accommodated in a common housing, the hydraulic lines also each require heaters, which have an adverse effect on cost and space and in an individual case must be procured from the automobile manufacturer with regard to the required specifications. in the other versions it is a prerequisite that each of the individual components, on their own, meet the demands made for a component mounted outside the passenger compartment with regard to splashproofness, fording ability or corrosion resistance. This can be extremely complicated, since in the SCR process, some of the components are actuated via levers, as in the case of the reversing valve for the pump. An eccentric drive mechanism may be actuated by an actuation magnet or an electric drive mechanism. These are not compact, rotationally symmetrically embodied individual components that operate independently of one another; on the contrary, they are components which are in engagement with one another in manifold ways. This makes separate sealing for each component, as is known in the second embodiment previously chosen and known from the prior art, extremely difficult. Moreover, heating the components of an SCR system that are accommodated outside a common mounting block and received there proves extremely difficult, especially with regard to heat transfer from a heat source to the individual components received on a common mounting block.